Ethylene glycol is a valuable material with a multitude of commercial applications. Monoethylene glycol (MEG) is used as a raw material in the manufacture of polyester fibres, polyethylene terephthalate (PET) plastics and resins. It is also incorporated into automobile antifreeze liquids.
In a typical industrial process, MEG is prepared in a two-step process. In the first step, ethylene is converted to ethylene oxide by reaction with oxygen over a silver oxide catalyst. The ethylene oxide can then be converted into MEG. This may be carried out directly by catalytic or non-catalytic hydrolysis. Alternatively, in one well-known process ethylene oxide is catalytically reacted with carbon dioxide to produce ethylene carbonate. The ethylene carbonate is subsequently hydrolysed to provide ethylene glycol.
These routes rely for their starting material on ethylene, which is produced in the petrochemical industry by steam cracking of hydrocarbons derived from fossil fuels. In recent years increased efforts have been focussed on reducing the reliance on fossil fuels as a primary resource for the provision of fuels and commodity chemicals. Carbohydrates and related ‘biomass’ are seen as key renewable resources in the efforts to provide new fuels and alternative routes to desirable chemicals.
In particular, certain carbohydrates can be reacted with hydrogen in the presence of a catalyst system to generate polyols and sugar alcohols. Current methods for the conversion of saccharides to glycols revolve around a hydrogenation/hydrogenolysis process. A process for the conversion of cellulose to products including MEG is described in Angew. Chem. Int. Ed. 2008, 47, 8510-8513. Continuous processes for generating at least one polyol from a saccharide-containing feedstock are described in WO 2013/015955 and CN 103731258A.
The products of these reactions are a mixture of materials comprising MEG, monopropylene glycol (MPG), 1,2-butanediol (1,2-BDO) and other by-products. Although the conversion of glucose to glycols can be carried out with high selectivity to MEG, a much lower selectivity and increased levels of MPG are obtained when using sucrose as a feedstock. MPG has a much more limited market demand than MEG. However, from an economic point of view, sucrose would be a more desirable starting material for this process.
It would be desirable to provide a process for the production of MEG from a bio-based feedstock in which the selectivity to MEG was increased and fewer, or more desirable, by-products were produced.